In a centrifugal separator which is provided with an energy transformation device of said kind, parts of the rotor of the centrifugal separator form an outlet chamber, in which liquid rotates. The outlet chamber is arranged to receive a separated liquid continuously from the separation chamber of the centrifugal rotor. This liquid forms a rotating liquid body in the outlet chamber. Centrally in the outlet chamber an outlet device is arranged, through which liquid is discharged out of the outlet chamber and further out of the centrifugal rotor. A centrifugal separator of this kind is shown in WO 88/7893, for instance.
In many cases it is important that the energy transformation device can transform as much as possible of the energy stored in the rotating liquid to pressure energy. How high a pressure that can be achieved as a maximum is determined by the equation of Bernoullis for the pressure along a flow line of the liquid. EQU P.sub.stat +P.sub.dyn =konst
The static pressure P.sub.stat at the inlet opening is composed by the pressure from the part of the rotating liquid body, which is located radially inside the inlet opening, and the pressure which acts on this part of the liquid body.
The dynamic pressure P.sub.dyn is in each point along a flow line determined by the equation EQU P.sub.dyn =1/2.rho.W.sup.2
in which .rho. is the density of the liquid and W is the flow rate of the liquid in the point looked upon.
Outside the inlet opening the liquid has a total pressure which is the sum of the static and dynamic pressure there. However, in the device in a centrifugal separator known by WO 88/7893 only a minor part of the dynamic pressure can be recovered in the form of a liquid pressure in the outlet. Therefore, another device has been suggested for separators for the recovery of the kinetic energy of the rotating liquid, which is to be discharged out of the chamber of the centrifugal rotor.